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MAX3243CWI Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX3243CWI Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 16 page 1µA Supply-Current, True +3V to +5.5V RS-232 Transceivers with AutoShutdown _______________________________________________________________________________________ 7 AutoShutdown A 1µA supply current is achieved with Maxim’s new AutoShutdown feature, which operates when FORCEON is low and FORCEOFF is high. When the MAX3221/MAX3223/MAX3243 sense no valid signal levels on all receiver inputs for 30µs, the on-board power supply and drivers are shut off, reducing supply current to 1µA. This occurs if the RS-232 cable is dis- connected or the connected peripheral transmitters are turned off. The system turns on again when a valid level is applied to any RS-232 receiver input. As a result, the system saves power without changes to the existing BIOS or operating system. When using AutoShutdown, the INVALID output is high when the device is on and low when the device is shut down. Because INVALID indicates the receiver inputs’ condition, it can be used in any mode (Figure 3). Table 2 and Figure 3c summarize the MAX3221/ MAX3223/MAX3243 operating modes. FORCEON and FORCEOFF override the automatic circuitry and force the transceiver into its normal operating state or into its low-power standby state. When neither control is assert- ed, the IC selects between these states automatically based on receiver input levels. Figures 3a, 3b, and 5a depict valid and invalid RS-232 receiver levels. A mouse or other system with AutoShutdown may need time to wake up. Figure 4 shows a circuit that forces the transmitters on for 100ms, allowing enough time for the Table 1a. MAX3221/MAX3223 F FO OR RC CE EO OF FF F and Enable Control Truth Table Table 1b. MAX3243 F FO OR RC CE EO OF FF F Control Truth Table Active* 1 1 Active* 0 1 F FO OR RC CE EO OF FF F High-Z 1 0 High-Z 0 0 T_OUT E EN N High-Z Active High-Z Active R_OUT +0.3V -0.3V INVALID TO MAX32_ _ POWER SUPPLY AND TRANSMITTERS R_IN * TRANSMITTERS ARE DISABLED, REDUCING SUPPLY CURRENT TO 1 µA IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR AT LEAST 30 µs. 30µs COUNTER R Active* 1 High-Z 0 T_OUT F FO OR RC CE EO OF FF F Active* High-Z R_OUT Active Active R2OUTB Figure 3a. MAX32_ _ Entering 1µA Supply Mode via AutoShutdown *Note: If the part is in AutoShutdown mode (FORCEOFF = VCC, FORCEON = GND), it is shut down if no valid RS-232 levels are present on all receiver inputs. FORCEON MASTER SHDN LINE 0.1µF 1M FORCEOFF MAX3221 MAX3223 MAX3243 POWER MANAGEMENT UNIT Figure 4. AutoShutdown with Initial Turn-On to Wake Up a Mouse or Another System +2.7V -2.7V INVALID TO MAX32_ _ POWER SUPPLY R_IN * TRANSMITTERS ARE ENABLED IF: ANY RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V. ANY RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR LESS THAN 30 µs. 30µs COUNTER R Figure 3b. MAX32_ _ with Transmitters Enabled Using AutoShutdown FORCEOFF POWER DOWN INVALID FORCEON INVALID IS AN INTERNALLY GENERATED SIGNAL THAT IS USED BY THE AUTOSHUTDOWN LOGIC AND APPEARS AS AN OUTPUT OF THE DEVICE. POWER DOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE OPERATIONAL STATUS OF THE TRANSMITTERS AND THE POWER SUPPLIES. Figure 3c. AutoShutdown Logic |
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